Letter to the Editor

Detection of DCO⁺ in a circumstellar disk

¹ Leiden Observatory, PO Box 9513, 2300 RA Leiden, The Netherlands
² Department of Physics & Astronomy, University College London, Gower Street, London WC1E 6BT, UK

Corresponding author: E. F. van Dishoeck ewine@strw.leidenuniv.nl

Received: 9 December 2002
Accepted: 21 January 2003

Abstract

We report the first detection of DCO⁺ in a circumstellar disk. The DCO⁺ line at 360.169 GHz is observed with the 15 m James Clerk Maxwell Telescope in the disk around the pre-main sequence star TW Hya. Together with measurements of the HCO⁺ and H¹³CO⁺  lines, this allows an accurate determination of the DCO⁺/HCO⁺ ratio in this disk. The inferred value of is close to that found in cold pre-stellar cores and is somewhat higher than that measured in the envelope around the low-mass protostar IRAS 16293–2422. It is also close to the DCN/HCN ratio obtained for pristine cometary material in the jet of comet Hale-Bopp. The observed DCO⁺/HCO⁺ ratio for TW Hya is consistent with theoretical models of disks which consider gas-phase fractionation processes within a realistic 2-D temperature distribution and which include the effects of freeze-out onto grains.